Promise.resolve()
    .then(() => {
        console.log("then1"); // 同步
        Promise.resolve()
            .then(() => {
                console.log("then1-1"); // 同
                return Promise.resolve();
            })
            .then(() => {
                console.log("then1-2"); // 微
            });
    })
    .then(() => {
        console.log("then2"); // 微
    })
    .then(() => {
        console.log("then3");// 微
    })
    .then(() => {
        console.log("then4");// 微
    });


/**
 * 输出结果：
 * then1
 * then1-1
 * then2
 * then3
 * then4
 * then1-2
 */
